Power conversion for distributed dc source array

ABSTRACT

Embodiments related to the conversion of DC power to AC power are disclosed. For example, one disclosed embodiment provides a power conversion system, comprising a plurality of direct current (DC) power sources, a plurality of power output circuits connected to one another in a parallel arrangement, each power output circuit being connected to a corresponding DC power source to receive power from the corresponding DC power source and to selectively discharge power received from the corresponding DC power source, a power combiner configured to combine power received from the plurality of power output circuits to form a combined power signal, an output stage configured to convert the combined power signal into an AC signal or a DC signal, and a controller in electrical communication with each power outlet circuit and the power combiner to control the output of power by the power converter.

BACKGROUND

Typical appliances and loads in residences, commercial use andindustries are run on alternating current (AC) power due to theefficiencies of usage, generation and distribution of AC power. As such,the use of power conversion devices is widely accepted for commercial orgrid power from independent direct current (DC) sources, such asbatteries and solar cells used to generate electrical power AND/or storeit for later use.

Many known power conversion devices utilize a DC source connected to acommutating or power conversion device bridge, which creates a square,stepped or sinusoidal voltage wave by using several switching devices.The DC power source is insulated from the AC output using layers ofcomponents such as switches and transformers. The generated voltage isfiltered and modified to match the grid requirements by the way ofnumber of feedback mechanisms such as pulse width modulation techniquesand filters.

FIG. 11 shows one example of a known power conversion device in the formof a power conversion bridge circuit 1100. Bridge circuit 1100 allows DCpower to be converted into AC power via manipulation of switches S1, S2,S3 and S4 to produce a desired AC output waveform. Table 1 illustrateshow the switching states of switches S1-S4 affect an output voltageV_(x) of bridge circuit 1100.

TABLE 1 Switch S1 Switch S2 Switch S3 Switch S4 V_(x) Comment ON OFF OFFON +V_(DC) Positive wave OFF ON ON OFF −V_(DC) Negative wave ON OFF ONOFF 0 Net zero OFF ON OFF ON 0 Net zero

With bridge circuit 1100, the use of appropriate switching sequence andtiming allows the creation of a desired waveform, and also allows thecontrol of harmonic content in the output waveform. Further, ripple andharmonics in the output signal may be filtered by using resonant loads,tank circuits, or external filters with band pass characteristics tolimit the presence of noise in output.

In some distributed DC networks, plural DC sources may be interconnectedin a series-parallel combination. The series combination of DC sourcesgives higher DC voltages and may be used to bring operational voltagesto desired levels. On the other hand, the overall power is increased bycombining multiple legs of sources in parallel.

However, one issue with a DC network of series-parallel combination isthat any individual source mismatch may lead to significant loss ofpower in the network. Specifically, any defect in one source throttlesthe output from all series-connected sources. Likewise, parallel legshaving sources with lower voltages may sink the power from other legsinstead of sourcing, and thus may reduce the overall output. This mayhappen in case of solar cells arrayed together, where the output from acell will be degraded or reduced due to shading of the cells. Even asingle cell which is shaded will reduce its own output, as well as theoutput of the module in which the cell is located. Likewise, a shadedmodule will reduce the output from a string of series-connected modules.In many solar installations, multiple strings of series-connectedmodules are paralleled together to achieve desired output power levels.Thus, the impact of a loss of power from a cell can be severe and resultin significant power loss for an entire solar cell array when connectedin this manner. Further, in some environments, even during normaloperation, there may be a statistical variation between the power outputfrom individual DC sources as high as ten percent.

SUMMARY

Accordingly, various embodiments are disclosed herein that relate to theconversion of DC power to AC power to address the above-describedissues. For example, one disclosed embodiment provides a powerconversion system, comprising a plurality of direct current (DC) powersources, a plurality of power output circuits connected to one anotherin a parallel arrangement, each power output circuit being connected toa corresponding DC power source to receive power from the correspondingDC power source and to selectively discharge power received from thecorresponding DC power source, a power combiner configured to combinepower received from the plurality of power output circuits to form acombined power signal, an output stage configured to convert thecombined power signal into an AC signal or a DC signal, and a controllerin electrical communication with each power outlet circuit and the powercombiner to control the output of power by the power converter.

This Summary is provided to introduce a selection of concepts in asimplified form that are further described below in the DetailedDescription. This Summary is not intended to identify key features oressential features of the claimed subject matter, nor is it intended tobe used to limit the scope of the claimed subject matter. Furthermore,the claimed subject matter is not limited to implementations that solveany or all disadvantages noted in any part of this disclosure.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a block diagram of an embodiment of a power conversionsystem.

FIG. 2 shows a block diagram of another embodiment of a power conversionsystem.

FIG. 3 shows a schematic diagram of an embodiment of a power conversionsystem that comprises an energy packet generator for each of a pluralityof DC sources.

FIG. 4 shows embodiments of an energy packet generator circuit and aportion of a combiner circuit, and also shows a timing diagramillustrating voltages at designated points in the circuit as a functionof time according to an embodiment of a method of operating the circuit.

FIG. 5 shows an embodiment of a combined energy packet signal prior toshaping to produce an output signal.

FIG. 6 shows a schematic diagram of an embodiment of a power conversionsystem that comprises a plurality of energy packet generators for eachof a plurality of DC sources.

FIG. 7 shows a schematic diagram of an embodiment of a power conversionsystem that comprises an output stage having a plurality oftransformers.

FIG. 8 shows an embodiment of a pulse sequence that may be used tooperate the embodiments of FIGS. 6 and 7.

FIG. 9 shows an embodiment of a power conversion system that comprises acapacitive output stage.

FIG. 10 shows a flow diagram depicting an embodiment of a method forconverting DC power from a plurality of DC power sources.

FIG. 11 shows a conventional power conversion circuit.

DETAILED DESCRIPTION

One potential issue with the power conversion bridge circuit 1100 shownin FIG. 11 is the variability of current as seen at the input DC source.This is especially of concern for DC sources such as solar cells, whichwork optimally near a point of maximum power. Another issue with powerconversion bridge circuit 1100 is that the filtering of harmonics maylead to loss of energy and reduction of efficiency of conversion.Further, the network of switches S1-S4 may require complex controls andfeedback mechanisms to ensure the synchronization of output to the loadas well maintain a sinusoid output and a maximal power output that aredesirable for variable loads.

Additionally, the arrangement of power conversion bridge circuit 1100does not account for the distributed nature of the DC sources. Thearrangement of circuit 1100 assumes that each source is independent ofothers, and that the delivery of the DC power to the bridge is lossless.However, in reality, the various DC sources may be interconnected in aseries-parallel combination, and are thus not independent of oneanother. As described above, an issue with a series-parallel combinationis that any source mismatch may lead to significant loss of power in thenetwork, as any parallel legs having sources with lower voltages maysink the power from other legs, and any shaded cell or module may reducethe output from a string of series-connected cells or modules. Further,another concern with the power conversion bridge circuit 1100 is thatthe photovoltaic module or solar cells are always ON, and thus present asafety hazard, as they are always outputting high voltages and/or havepotential of a short circuit induced arcing.

Thus, embodiments are disclosed here that address at least these issueswith the conversion of DC power into AC power. Further, the disclosedembodiments may be used with distributed and plural DC power sources,including but not limited to batteries, solar cells, supercapacitors,fuel cells, and other such distributed power generation sources. FIG. 1shows an example embodiment of a power conversion system 100. Powerconversion system 100 comprises a plurality of DC power sources, shownas DC power source 1 102, DC power source 2 104, and DC power source N106, wherein N illustrates that any suitable number of DC power sourcesmay be utilized. Each power source is electrically connected to a poweroutput circuit. These are illustrated as power output 1 108, poweroutput 2 110, and power output N 112. Where the DC power sourcesrepresent solar cells, each DC power source 102, 104, 106 may comprise asingle solar cell, or multiple solar cells connected in series and/orparallel. Further, the DC power source may comprise a mix of battery,super-capacitors, solar cells, and/or fuel cells in various embodiments.

Power that is output by power outputs 108, 110 and 112 is directed to apower combiner 114, which combines the individual power outputs into asingle combined power signal at 116. The combined power output signalmay then be directed to an output stage 118, which may includewaveform-generating circuits configured to generate a desired waveformfrom the combined power signal, as well as filters (e.g. for removingany undesired harmonic frequencies), matching networks, transformers,and/or other conditioning systems, such as a power grid synchronizationsystem. Depending upon the specific configuration of the output andfilter conditioning stage 118, the output may take the form of a DCsignal 120 or an AC signal 122. Further, as described below, in someembodiments, power received from each of power output circuits by thepower combiner may be substantially of a same polarity, thereby allowingsource isolation and AC output formation without the use of a bridgecircuit such as that shown in FIG. 11. The term “substantially of a samepolarity” indicates that the power output by the power output circuitsis not inverted with a bridge circuit to help produce a negativehalf-cycle of an AC signal, as is done with the circuit of FIG. 11.

The use of power outputs 108, 110, 112 to provide power from each DCpower source 102, 104, 106 allows the flow of power from each powersource to be individually controlled. In turn, this permits the use ofembedded control logic or other control logic to be used to control andcombine power that is output by power outputs 108, 110, 112 in such amanner as to efficiently provide desired power to a load. Examples ofsuch logic are illustrated schematically in FIG. 1 as an array powercontrol circuit 130, an array combiner control circuit 132, and anoutput control and synchronization circuit 134.

As depicted, the array power control circuit 130 is configured tomonitor the output of each DC power source 102, 104, 106, and to controlthe output of power by power outputs 108, 110, 112 in response. In thismanner, the amount of power provided by power outputs 108, 110, 112 tothe power combiner 114 may be adjusted to compensate for any variationin the power produced by DC power sources 102, 104, 106. As a morespecific example, where each DC power source 102, 104, 106 comprises oneor more solar modules, a decrease in the output of one module due tocloud cover may be compensated by adjusting the operation of the poweroutputs. Further, the use of power outputs 108, 110, 112 allows each DCpower source to be isolated from other DC power sources. This allows,for example, a DC power source that experiences a temporary decrease inpower generation (e.g. due to cloud cover) to be electrically isolatedfrom other DC power sources, and therefore may help to prevent sinkingpower into sources that are operating at lower power. It will beunderstood that the specific feedback and control connections for arraypower control circuit 130 are shown for the purpose of example and arenot intended to be limiting in any manner, as the array power controlcircuit 130 may use any suitable information to control the poweroutputs 108, 110, 112.

The combiner control circuit 132 is depicted as monitoring the outputsof each power output 108, 110, 112, and as receiving feedback from theoutput and filter conditioning stage 118 and output control andsynchronization circuit 134. Further, the combiner control circuit 132also may receive feedforward from the array power control circuit 130 toobtain information regarding what outputs to expect from the individualpower sources, and then use such information to correct for outputpower. With such feedback and feedforward information, the arraycombiner control circuit 132 controls the output of the power combinercircuit 114 in response. For example, the array combiner control circuit132 may be configured to control various tunable components in the powercombiner circuit 114. Such components may be adjusted to optimize theperformance of the power combiner circuit 114 based upon such quantitiesas a frequency, magnitude, or other characteristic of an output signalreceived from each power output 108, 110, 112, and/or a characteristicof the performance of the output and filter conditioning stage 118, forexample. It will be understood that the particular feedback and controlconnections to and from the array combiner control circuit 132 that aredepicted in FIG. 1 are shown for the purpose of example and are notintended to be limiting in any manner, as the array combiner controlcircuit 132 may use any suitable inputs to control the combination ofpower signals received from power outputs 108, 110, 112.

The output control and synchronization circuit 134 is depicted asmonitoring the output of the output and filter conditioning stage 118(example outputs are depicted as DC output 120 and AC output 122), andproviding feedback control to the output filter and conditioning stage118. For example, the output control and synchronization circuit 134 maybe configured to form a desired AC waveform, and to synchronize theoutput of the output and filter conditioning stage 118 to an externalpower grid. The output control and synchronization circuit 134 also mayprovide information to the array combiner control circuit 132 forcontrol of the power combiner circuit 114. It will be understood thatthe particular feedback and control connections to and from the arraycombiner control circuit 134 depicted in FIG. 1 are shown for thepurpose of example and are not intended to be limiting in any manner, asthe array combiner control circuit 134 may use any suitable inputs tocontrol the operation and output of the output and filter conditioningstage 118.

The array power control circuit 130, the array combiner control circuit132, and the output control and synchronization circuit 134 each mayinclude various logic components, and/or may be controlled by externallogic. Such logic may reside locally, and/or may reside at a remotelocation accessible via a network (not shown). Such logic is representedin FIG. 1 collectively as a controller 140 that comprises a processor142, and memory 144 comprising instructions executable to perform thevarious tasks related to the control of power conversion system 100.Such instructions may reside in computer-readable media such asnon-transitory memory, examples of which include but are not limited tovarious types of RAM, ROM, and mass storage. Such instructions also mayreside also may reside on a removable computer-readable medium,including but not limited to removable hard drive, DVD, CD-ROM, Flashmemory drive and/or other such solid state memory, and/or any othersuitable removable computer-readable media. While the controller 140 isdepicted in FIG. 1 as a separate component from control circuits 130,132 and 134, it will be understood that the control circuits 130, 132,134 may be implemented partially or fully as executable instructionswithin controller 140.

The embedding of control logic with power sources as illustrated in FIG.1 may enable information about the instantaneous condition of the powersource to be used to adjust and modify the amount of power to be takenfrom each source and thus optimally from the array. In addition, the useof appropriate central logic may help to ensure the power flows in thearray so as to maximize the efficiency of the overall array.Additionally, the separation of controlling the power flow fromindividual sources, from the combiner, and from the output controlcircuitry allows the array to be able to maximally transfer power tovariety of loads, including AC and/or DC loads. Further, the use ofpower outputs connected to each DC power source allows power from the DCsources to be completely turned off when desired or required. This mayenable safe handling and storage of the DC power sources 102, 104, 106as the output may be configured not to carry any high voltages orpresent a risk of arcing.

The embodiment of FIG. 1 also may be used as a charge controller for abattery bank. In this case, the power conversion system 100 may be usedas an inverter for AC loads as well as a charge controller for a batterybank that could be utilized to supply power to AC loads when solar poweris unavailable, and/or to supplement solar power when it is insufficientto run such AC loads.

The power outputs 108, 110, 112 may be configured to output any suitablesignal to the power combiner circuit 114, and may include any suitablecomponents. For example, in some embodiments, the power outputs may beconfigured to generate energy packets for combination into a desiredwaveform. FIG. 2 depicts an example of an embodiment of a powerconverter 200 configured to utilize the generation of energy packets forcombination into a desired output signal. The terms “energy packet” and“electrical energy packet” as used herein represents a discrete outputof energy such that the power output is non-zero for a duration and zerofor a duration that is greater than a mere crossing of a zero voltageduring a rising or falling transition. The duration of zero output fromone energy packet generator may occur, for example, while another energypacket generator is currently providing a non-zero output. This mayallow isolation of one DC power source from another that is connected ina parallel arrangement via energy packet generators.

Power converter 200 is shown as comprising an arbitrary number N of DCpower sources, illustrated as V₁ 202, V₂ 204, and V_(N) 206. Further,power converter 200 also comprises an energy packet generatorcorresponding to each DC power source. These are illustrated as energypacket generators 208, 210 and 212, which respectively correspond to DCpower sources 202, 204 and 206. Each energy packet generator, asdescribed in more detail below, is configured to selectively generate anelectrical energy packet for provision to an energy packet combiner,which is configured to receive electrical energy packets from theplurality of energy packet generators and to combine the electricalenergy packets into a combined energy packet signal for production of anoutput signal by an output stage.

The use of energy packet generators 208, 210 and 212 allows each DCpower source 202, 204, 206 to be isolated from the other DC powersources, yet to achieve the output power of a parallel arrangement. Thismay allow a desired output power to be achieved, while also avoidingsinking power into any DC power source that is operating at a lowerpower level than others. Further, where one or more DC power sources arenot operating at a desired power level, the energy packet generatorcontrol circuit may compensate by adjusting the operation of the energypacket generators 208, 210, 212 to optimize the power that is input intothe packet combiner circuit 214 based upon the current state andcapabilities of the DC power sources 202, 204, 206.

The energy packet combiner circuit 214 may be configured to combine theenergy packets in any suitable manner to provide a desired output. Forexample, in the case where it is desired to output an AC signal, theenergy packet combiner circuit 214 may combine energy packets from eachenergy packet generator into a combined energy packet signal forprovision to an oscillating circuit. The combined energy packet signalmay have a frequency of energy packets, or a range of frequencies(spread spectrum), configured to drive oscillation of the circuit toproduce a desired output Likewise, a width of the energy packets may bemodulated to achieve a desired AC output. As a more specific example,where an AC output is desired, the energy packet combiner circuit 214may be configured to produce a combined energy packet signal forprovision to an LC tank circuit with a resonant frequency that ismatched to a frequency of a power grid 220 to which the power converteris coupled, or matched to a harmonic of the grid whereby the resonantfrequency of the circuit is an integral multiple of the power linefrequency. Due to the impedance characteristics of an LC tank circuit atits resonant frequency, power from DC power sources 202, 204, 206 may beefficiently provided to a load compared to the circuit of FIG. 11. Itwill be understood that the term “matched to a frequency” and the likeas used herein may refer to any suitable frequency configured to cause adesired response in an oscillating circuit, and encompasses frequenciesmatched to fundamental frequencies as well as harmonic frequencies. Asnon-limiting examples, the frequency may be double or ten times thepower line frequency, or may be any other suitable integral multiple ofthe grid frequency.

More generally, in some embodiments, the frequency of energy packetsemitted from each energy packet generator may be some integer L timesthe resonant frequency of the oscillating circuit, as each energy packetgenerator may generate L energy packets in one cycle. Likewise, theresonant frequency of the oscillating circuit may be m integer times thegrid frequency. Thus, if there are N energy packet generators configuredto emit electrical energy packets in a staggered timing in one resonantcycle, then the width of each energy packet may be, for example,1/(resonant frequency *L*N)=1/(grid frequency*m*N*L).

A combiner control circuit 232 and a grid synchronization circuit 234may be used to control the frequency, phase, and/or othercharacteristics of the output of the power converter 200. Further, asdescribed above in the context of FIG. 1, the power conversion systemmay comprise logic, represented as controller 240, in electricalcommunication with each energy packet generator and the energy packetcombiner to control the generation and combination of electrical energypackets.

Any suitable circuitry may be used to control the generation andcombination of energy packets. For example, some embodiments may employa switched network of elements including capacitors, inductors,resistors, and switches to convert power from an array of DC sourcesinto energy packets, and to combine the energy packets into a desiredoutput.

FIG. 3 shows an embodiment of a power converter 300 comprising such aswitched network of elements. Power converter 300 is shown as comprisingan arbitrary number N of DC power sources (illustrated as V₁ 302, V₂304, and V_(N) 306). Further, power converter 300 also comprises anenergy packet generator corresponding to each DC power source, one ofwhich is shown at 308 as including an initial energy storage stage 310and a first switching stage 312. Additionally, power converter 300comprises an energy packet combiner 313 that includes, for each DC powersource 302, 304, 306, an intermediate energy storage stage 314 locatedbetween the first switching stage 312 and a second switching stage 316.

The initial energy storage stage 310 and the intermediate energy storagestage 314 are depicted as capacitors in FIG. 3, but it will beunderstood that any other suitable energy storage mechanism may be used,including but not limited to inductors and LC circuits. Likewise, firstswitching stage 312 and second switching stage 316 are each depicted asMOSFETs in FIG. 3, but it will be understood that any other suitableswitching mechanism may be used. Examples include, but are not limitedto, other FETs, bipolar junction transistors, thyristors, gatecontrolled thyristors, silicon controlled rectifiers, and/or otherelectronic switching devices.

The first switching stage 312 and the second switching stage 316 arerespectively electrically connected to the energy packet generatorcontrol circuit 317 and an energy packet combiner control circuit 328(which, as described above, may reside on a single controller or onseparate controllers). The energy packet generator control circuit 317and energy packet combiner control circuit 328 are configured control asequence of the opening and closing of the first switching stage 312 andsecond switching stage 316 for each DC power source.

FIG. 4 shows a timing diagram that illustrates an embodiment of a methodfor controlling the opening and closing of the first switching stage 312and the second switching stage 316 to produce an output signalcomprising a plurality of temporally spaced energy packets. Generally,according to the embodiment of FIG. 4, for each DC power source, thefirst switching stage 312 and second switching stage 316 are operated ina first energy packet production phase in which the first switchingstage 312 is in a closed state and the second switching stage 316 is inan open state to pass charge from the DC power source 302 to theintermediate charge storage stage 314. Then, the first and secondswitching stages are operated in a second energy packet production phasein which the first switching stage 312 is in an open state and thesecond switching stage 316 is in a closed state to discharge anelectrical energy packet that is combined with energy packets from otherenergy packet generators to form a combined energy packet signal for theoutput stage 320. In this manner, the output stage 320 is electricallyisolated from the DC power source 302 throughout operation. Further, bysequencing this operation for each of the plurality of DC power sources,each DC power source may be made independent from the other DC powersources so that a source that is operating at a lower power output willnot sink current from other DC power sources.

The nature of this operation can be seen via the timing diagramsillustrated in FIG. 4, which show voltages in the depicted circuit as afunction of time. The voltage at point A in the circuit (the initialenergy storage stage) is shown as V_(A), the voltage at point B (thegate of the first switching stage) as V_(B), the voltage at point C (theintermediate energy storage stage) as V_(C), the voltage at point D (thegate of the second switching stage) as V_(D), and the voltage at point E(the output of the energy pulse combiner stage) as V_(E).

First, the DC power source 302 provides current that is output to theinitial energy storage stage 310. The sequence of transfer of energy iscontrolled by controlling the first and second switching stages viacontrol pulses applied at points B and D to transfer the energy from theDC power source 302 to the output stage 320, and thus to a load. V_(B)and V_(D) illustrate a repetitive, time delay switching between controlpulses at the first switching stage 312 and the second switching stage316, respectively. It can be seen that, in the initial state of thetiming diagram 400, a low logic state is applied to the second switchingstage 316 while a high logic state is applied to the first switchingstage 312. Thus, the second switching stage 316 is in an open statewhile charge is transferred through the first switching stage 312 to theintermediate energy storage stage 314. Thus, it further can be seenthat, during this phase of operation, the voltage at the initial energystorage stage 310 (V_(A)) decreases while the voltage at theintermediate energy storage stage 314 (V_(C)) increases. Also, thevoltage V_(E) at the output of the second switching stage 316 remainslow during this phase of operation.

Next, referring again to V_(B) and V_(D), it can be seen that V_(B) isperiodically reduced to logic low, thereby opening the first switchingstage 312. Then, V_(D) is pulsed to logic high, thereby closing thesecond switching stage 316 and thus producing an energy packet at theoutput of the second switching stage 316, as shown at V_(E). A delay maybe used between the opening of the first switching stage 312 and theclosing of the second switching stage 316. In the depicted embodiment,V_(D) is pulsed to logic high for a relatively narrow window, therebyleading to the creation of an output energy packet which is narrow andsharp. Examples of suitable ranges for the width of the energy packetinclude, but are not limited to, widths in a range of 10 nanoseconds to5 milliseconds. Likewise, examples of suitable frequencies of energypackets in the combined energy packet signal include, but are notlimited to, frequencies within a range of 100 Hz to greater than 100MHz. It will be understood these ranges are presented for the purpose ofexample, and that an energy packet may have any other suitable shape andwidth, and that a combined energy packet signal may have any othersuitable frequency or frequencies. Further, it will be understood thatthe combined energy packet signal frequency or frequencies, and/or theenergy packet width, may be variable over time as the energy packetgenerators and/or combiner are adjusted based upon current DC powersource output characteristics to help achieve desired outputefficiencies.

By utilizing a delay between the opening of the first switching stage312 and the closing of the second switching stage 316, the DC powersources are insulated from a load. Further, operating the first andsecond switching stages as depicted in FIG. 4 may allow the DC powersource 302 source to remain balanced, as the second switching elementconnects the load only for a window and transfers the most electricalenergy in the form of a pulse. For example, maintaining DC power source302 connected to the initial energy storage stage 310 at all timesserves to balance the DC power source 302, as initial energy storagestage 310 helps to smooth variation in effective loading and therebyhelp to establish reliable and efficient functioning of the DC powersource 302.

In the depicted embodiment, the window for connecting the initial energystorage stage 312 to the intermediate energy storage stage 316 iscontrolled by the width of the high logic stages in the V_(B) timingdiagram. In this embodiment, this window is kept relatively wide, andmay range in width from, for example, 10 nanosecond to 10 milliseconds,depending on the frequency of the combined energy packet signal. Forexample, where a power line has a frequency of 50 or 60 Hz, the firstswitching stage may be controlled with a pulse width of approximately 10ms, while higher frequency of 100 MHz may utilize pulses ofapproximately 10 ns widths. Such AC pulses may essentially have a dutycycle value of between 0.5 to 0.999999, thereby leading to the DC powersource 302 being connected to the initial energy storage stage 310 andthe intermediate energy storage stage 314 for a majority of time.

During this time any energy output by DC power source 302 is beingstored in initial energy storage stage 310 and intermediate energystorage stage 314. Next, when V_(B) pulses low to open the firstswitching stage 312, the intermediate energy storage stage 314 is nolonger connected to the DC power source 302, while the initial energystorage stage 312 continues to be connected to the DC power source 302.During this time the initial energy storage stage 312 is being fed theenergy from DC power source 302 and continues to store it. Next, thelogic high pulse of V_(D) connects the intermediate energy storage stage314 to an output load via the second switching stage 316. Theintermediate energy storage stage 314 then transfers its stored energyto the output load. This discharging of the intermediate energy storagestage 314 is then stopped when the second switching stage opens (e.g.when V_(D) transitions to logic low). This leads to the load beinginsulated and stops any discharging of the second energy storage stage314. With the repetition of the cycle where the DC power source 302 andthe initial energy storage stage 310 are connected to the intermediateenergy storage stage 314, the energy lost by the intermediate energystorage stage 314 is replenished. In this manner, the cycle continueswith the repeating transfer of energy. It will be understood that theembodiment of FIG. 4 is presented for the purpose of example, and is notintended to be limiting in any manner, as any other suitable pulsetiming may be used to control the first switching stage 312 and thesecond switching stage 316.

The initial energy storage stage 310 may be configured to have anysuitable energy storage capacity. For example, in some embodiments, inorder to balance the DC power source 302, the initial energy storagestage 310 may be configured to drain 10% or less of stored charge whilethe first switching stage 312 is closed, as this may help to maintainbalance of the DC power source 302. In other embodiments, the initialenergy storage stage 310 may have any other suitable energy storagecharacteristics. Likewise, the intermediate energy storage stage 316also may have any suitable energy storage characteristics. For example,the intermediate energy storage stage may be configured to havesufficient storage capability to allow the isolation of the DC powersource 302 from the output and provide the desired higher powercapability for instantaneous pulsing out of large amounts of energy.

FIG. 5 illustrates an embodiment of a method of sequencing an energypacket generation timing for four energy packet signals 500, 502, 504,506 produced via four energy packet generators (such as depicted inFIGS. 6 and 7, described in more detail below). It will be understoodthat the concepts illustrated in this figure may be extended to anysuitable number of energy packet generators. The energy packets fromeach energy packet generator are temporally staggered such that acombined energy packet signal 508 formed from the combination of eachindividual energy packet signal comprises a frequency approximately Ntimes higher than the frequency of any individual energy packet signal,wherein N is the number of energy packet generators. The combined energypacket signal 508 may have any suitable energy packet frequency.Suitable frequencies include those that are configured to produce adesired output signal in a downstream output stage.

As a more specific example, the combined energy packet signal may have afrequency matched to a resonant frequency of an oscillating circuit,such as a tank circuit, to thereby create an alternating currentwaveform output via the tank circuit. The resonant frequency (F001) ofthe tank circuit determines the frequency of each combined energy packetsignal pulse train (F002) which may, for example, be eitherapproximately equal to or be an integral multiple of the resonantfrequency. In other words,

F002=F001, or

F002=n* F001 where n is an integer 1, 2 3 . . . .

Thus, if there are N independent sources and when the frequency F002equals F001, the pulse width PW of each source (i.e. the width of theenergy packet from each source) is narrower than 1/(F002*N).

As a more specific example, for a resonant circuit working at 50 Hz(i.e. matched to a 50 Hz power line), and where 100 energy packetgenerators are connected together, the pulse width for would be 19microseconds for the wide pulse that controls the first switching stage,and 1 microsecond for the narrow pulse that controls the secondswitching stage.

As another more specific example, the combined pulse signal may beconfigured to produce a desired DC signal via an RC circuit or othersuitable circuit.

Returning briefly to FIG. 3, an example output circuit is shown at 320as an oscillating circuit in the form of an LC tank circuit comprisingan inductor 322 and a capacitor 324. In the depicted embodiment, thecapacitor is depicted as being tunable. In other embodiments, theinductor may be tunable, and/or the capacitor may have a fixed value.Further, an output circuit also may have other components not shown inFIG. 3.

The LC tank circuit formed by inductor 322 and capacitor 324 isconfigured to be excited by the combined energy packet signal receivedfrom energy packet combiner 313 to cause oscillation at a resonantfrequency, thereby forming an AC waveform 326. Thus, the values of C andL for the capacitor 324 and inductor 322 may be selected to resonate ata desired frequency, such as at a frequency or harmonic of a power gridto which the power converter 300 is connected. Additionally, an AC gridsynchronization circuit 328 may be provided to synchronize thealternating current waveform from the output stage with a localelectrical grid. It will be understood that any other suitableoscillating circuit than the depicted LC circuit may be used to producethe AC waveform output. It further will be understood that the LC tankcircuit may be connected to a load with appropriate filtering,transformers, matching subsystems, etc., that are not shown herein.

The operation of the embodiment of FIG. 3 according to the methodsdepicted in FIGS. 4 and 5 to generation time-displaced combinations ofenergy packets may lead to transfer of essentially all the power fromthe distributed DC power sources in a manner to pump the tank circuitwith appropriate excitation pulses to transfer out a large quantity ofpower. The pulse generation sequence and the switching sequence arecontrolled using the energy packet generator control circuit and energypacket combiner control circuit. Further, feedback may be utilized fromthe output to allow the controller circuits to be programmed tosynchronize with a grid, to track load requirements, and/or change theoutput as needed.

In the embodiment of FIG. 3, each DC power source is connected to onecorresponding energy packet generator. However, in other embodiments,each DC power source may be connected to a corresponding plurality ofenergy packet generators. For example, FIG. 6 shows an embodiment of apower converter 600 in which each DC power source (shown as DC powersources V₁ 602 and V_(N) 604) provides power to two corresponding energypacket generators. These are illustrated as energy packet generators 606and 608 corresponding to power source 602, and energy packet generators610 and 612 corresponding to power source 604. As depicted, energypacket generators 606 and 608 utilize separate first switching stages(shown at 614 and 616, respectively), but share a common initial energystorage stage 618 (which may represent one or more capacitors,inductors, etc.). Energy packet generators 610 and 612 also utilizeseparate first switching stages and a common initial energy storagestage.

The four depicted energy packet generators 606, 608, 610, 612 are eachconnected to a corresponding intermediate energy storage stage andsecond switching stage, as represented by second energy storage stage620 and second switching stage 622. A combined energy packet signal fromthe four energy packet generators is then provided to an output stage,such as the depicted LC tank circuit 624 to provide an AC output. Inother embodiments, the combined energy packet signal may be provided toan output stage configured to form a voltage-controlled DC output, orany other suitable output.

FIG. 7 depicts an embodiment of a power converter 700 that is similar tothat of FIG. 6 in that power converter 700 comprise two energy packetgenerators for each DC power source. However, power converter 700utilizes transformers 702 to isolate each second switching stage 704from the output stage 706. The transformers 702 also act as inductors toform a tank circuit with capacitor 708. Thus, as depicted, eachtransformer 702 comprises a first coil connected to a correspondingsecond switching stage 704, and a second coil that, in combination withthe second coils of other transformers, forms the tank circuit with thecapacitor 708.

The use of a plurality of energy packet generators connected to each DCpower source allows the DC power source to continually provide output,and also further isolates the DC power sources from potentialfluctuations at the output. Further, with the appropriate controlling ofswitching such that each transfer function is mutually exclusive of theother, the overall loading on the DC power sources may be balanced, andsuch balancing may be better controlled with a greater number ofconnected transfer switches. Yet another advantage of the embodiments ofFIGS. 6 and 7 is that the requirement for energy storage stages may bereduced, as the overall load is balanced on the sources via appropriatesequence controls. While the embodiments of FIGS. 6 and 7 show twoenergy packet generators connected to each DC power source, it will beunderstood that any suitable number of energy packet generators, such as3 or more in some embodiments, may be connected to a DC power source.

FIG. 8 shows an embodiment of a timing diagram 800 illustrating pulsesequences suitable for controlling the embodiments of FIGS. 6 and 7 toproduce, for example, the combined energy packet signal shown at 508 inFIG. 5. First, FIG. 8 illustrates two control signals, at 802 and 804,that may be used to produce the pulse patterns applied to each firstswitching stage and second switching stage. The pulse patterns appliedto each first and second switching stage are shown for the four depictedenergy packet generators at 806, 808, 810, and 812. In these pulsepatterns, the top pulse pattern may be applied to the first switchingstage, while the bottom pulse pattern may be applied to the secondswitching stage. It will be noted that the pulse patterns 806, 808, 810and 812 are temporally shifted relative to one another to thus form adesired pattern of energy packets for combination. In the depictedembodiment, the pulses 814, 816, 818, 820 for each second switchingstage are temporally non-overlapping, such that the resulting energypackets are substantially non-overlapping. However, in otherembodiments, the pulse patterns may be configured to create at leastsome overlap between energy packets. It will be understood that therelative timing and pulse width for each pulse pattern may be controlledvia feedback obtained by monitoring the power converter output, each DCpower source, and/or any other suitable quantities.

FIG. 9 illustrates another embodiment of a power converter 900. Powerconverter 900 is similar to power converter 300 of FIG. 3 in that eachDC power source is connected to one corresponding energy packetgenerator. However, the output stage for the power converter 900 isconfigured to produce a DC output, rather than an AC output. As such,power converter 900 comprises a capacitive stage, represented bycapacitor 902, instead of an LC tank circuit, as an output stage. Thecapacitor 902 may combine with resistive elements in the circuit (notshown) to form an RC circuit with a time constant sufficient to producea DC output 904 from an input of a combined energy packet signal such asthat shown at 508 in FIG. 5. The capacitor 902 is shown as beingvariable, but a capacitor of fixed value also may be used. It will beunderstood that other components not shown may be used to smooth anyripple and further filter the DC output. Further, it will be understoodthat some embodiments may be configured to selectively output both DCand AC signals, as illustrated in FIGS. 1-2.

FIG. 10 shows an embodiment of a method 1000 for converting power froman array of direct current power sources to alternating current power.Method 1000 comprises, at 1002, converting DC power from each DC powersource to a series of electrical energy packets, and then at 1004,combining the series of electrical energy packets from each DC powersource to form a combined electrical energy packet signal. Thegeneration and combination of energy packets may be performed in anysuitable manner, including but not limited to those discussed above withreference to the embodiments of FIGS. 1-9. Further, as described above,the combined energy packet signal may have any suitable frequency, andthe energy packets may have any suitable width and magnitude, dependingupon a desired output signal to be formed. Next, at 1006, method 1000comprises directing the combined electrical energy packet signal into anoscillating circuit to drive the oscillating circuit, and at 1008,producing an alternating current (AC) output signal via the oscillatingcircuit. In some embodiments, as illustrated at 1010, the AC outputsignal may be synchronized with a power grid. It will be understood thata similar method may be used to produce a DC output signal, except thatan RC circuit may be used in place of a tank circuit to convert thecombined electrical energy packet signal into a DC signal.

Any suitable circuit oscillating circuit may be used to produce an ACwaveform. For example, in some embodiments as described above, a tankcircuit comprising inductive and capacitive components may be used toconvert a combined energy packet signal into a sinusoidal output signal.In such embodiments, a frequency of the energy packets in the combinedenergy packet signal may have a frequency matched to a resonantfrequency of the oscillating circuit, or may have any other suitablefrequency.

Likewise, any suitable method may be used to produce the electricalenergy packets. For example, as described above, converting DC powerfrom each DC power source to a series of electrical energy packets maycomprise, for each DC power source, operating a first switching stage ina closed state while operating a second switching stage in an open statethereby charging an intermediate charge storage stage located betweenthe first switching stage and the second switching stage, and thenoperating the second switching stage in a closed state while operatingthe first switching stage in an open state to release an electricalenergy packet from the intermediate storage stage. Further, charging theintermediate charge storage stage may comprise transferring electricalcharge from an initial charge storage stage to the intermediate storagestage while the first switching stage is in the closed state.

Via the above-described embodiments, power may be provided from eachsource controlled by each energy packet generator in a manner as toprovide suitable timing and magnitude of the energy packets. Further,the generated energy packets may be combined in such a manner as tooptimally collect and transfer the power. Additionally, the energycombiner circuitry may be variably and programmatically controlled as tocombine the pulses in a manner to provide suitable outputcharacteristics. The same combiner methodology can be used to provideand output which is voltage controlled DC, or AC that can have themagnitude and frequency independently controlled. Selection of anappropriate combination of energy packets may allow the energy packetgenerator and energy packet combiner control circuits to produce anysuitable output characteristics. It will be understood that outputshaping filtering and control circuitry may be used to stabilize theoutput waveform and remove any noise and/or unwanted distortion orharmonics. It will further be understood that feedback from either fromthe grid or load may be used to modify the control signals to help tomaintain a desired efficiency and performance.

It is to be understood that the configurations and/or approachesdescribed herein are presented for the purpose of example, and thatthese specific embodiments are not to be considered in a limiting sense,because numerous variations are possible. The subject matter of thepresent disclosure includes all novel and nonobvious combinations andsubcombinations of the various processes, systems and configurations,and other features, functions, acts, and/or properties disclosed herein,as well as any and all equivalents thereof.

1. A power conversion system, comprising: a plurality of direct current(DC) power sources; a plurality of energy packet generators, each energypacket generator being connected to a corresponding DC power source toreceive power from the corresponding DC power source and to selectivelygenerate an electrical energy packet; an energy packet combinerconfigured to combine electrical energy packets from the plurality ofenergy packet generators; and a controller in electrical communicationwith each energy packet generator and the energy packet combiner tocontrol the generation and combination of electrical energy packets. 2.The power conversion system of claim 1, wherein each DC power sourcecomprises one or more solar cells.
 3. The power conversion system ofclaim 1, wherein each DC power source comprises one or of a battery, asupercapacitor, and a fuel cell.
 4. The power conversion system of claim1, wherein each energy packet generator comprises a first switchingstage in electrical communication with the corresponding DC powersource, and wherein the energy packet combiner includes, for each DCpower source, a second switching stage located electrically between thefirst switching stage and the energy packet combiner, and anintermediate charge storage stage located between the first switchingstage and the second switching stage.
 5. The power conversion system ofclaim 4, wherein each energy packet generator further comprises aninitial charge storage stage located electrically between the firstswitching stage and the corresponding DC power source.
 6. The powerconversion system of claim 4, further comprising an output stage, andwherein, for each DC power source, the controller is configured tooperate the first switching stage and the second switching stage in afirst energy packet production phase in which the first switching stageis closed and the second switching stage is open to charge theintermediate charge storage stage, and then to operate the firstswitching stage and the second switching stage in a second energy packetproduction phase in which the first switching stage is open and thesecond switching stage is closed to emit an electrical energy packet tothe output stage.
 7. The power conversion system of claim 6, whereineach energy packet generator further comprises an initial charge storagestage disposed electrically between the first switching stage and thecorresponding DC power source, and wherein the initial charge storagestage comprises a capacitor configured to drain 10% or less of storedcharge during the first energy packet production phase.
 8. The powerconversion system of claim 6, wherein the controller is configured tosequence an energy packet generation timing for the plurality of energypacket generators.
 9. The power conversion system of claim 4, whereineach DC power source is connected to a corresponding plurality of energypacket generators each having an intermediate charge storage stage. 10.The power conversion system of claim 1, further comprising an outputstage comprises an oscillating circuit configured to produce the outputsignal in the form of an alternating current waveform.
 11. The powerconversion system of claim 10, wherein the output stage comprises an LCtank circuit.
 12. The power conversion system of claim 11, furthercomprising a plurality of transformers, each transformer comprising afirst coil connected to a corresponding second switching stage and asecond coil connected to the output stage.
 13. The power conversionsystem of claim 10, wherein the oscillating circuit comprises a resonantfrequency matched to a resonant frequency of a local electrical grid.14. The power conversion system of claim 13, further comprising an ACsynchronization circuit configured to synchronize the alternatingcurrent waveform from the output stage with a local electrical grid. 15.The power conversion system of claim 10, wherein the controller isconfigured to control the generation of energy packets to direct acombined energy packet signal having a frequency matched to a resonantfrequency of the oscillating circuit into the oscillating circuit.
 16. Apower conversion system, comprising: a plurality of direct current (DC)power sources; a plurality of energy packet generators, each energypacket generator being connected to a corresponding DC power source andeach energy packet generator comprising a first switching stageconfigured to pass power from the corresponding DC power source when ina closed state, an initial charge storage stage disposed electricallybetween the first switching stage and the corresponding DC power source;an energy packet combiner comprising, for each DC power source, a secondswitching stage, and an intermediate charge storage stage disposedbetween the first switching stage and the second switching stage, theintermediate charge storage stage being configured to receive and storecharge when the first switching stage is in a closed state and thesecond switching stage is in an open state, and to be electricallyisolated from the corresponding DC power source and to emit anelectrical energy packet when the first switching stage is in an openstate and the second switching stage is in a closed state; an outputstage configured to receive a sequence of energy packets from the energypacket generators and to produce an output signal from the sequence ofenergy packets; and a controller configured to control the generation ofthe sequence of electrical energy packets.
 17. The power conversionsystem of claim 16, wherein each DC power source comprises one or moreof a solar cell, a battery, a supercapacitor, and a fuel cell.
 18. Thepower conversion system of claim 16, wherein each DC power source isconnected to a corresponding plurality of energy packet generators eachhaving an intermediate charge storage stage.
 19. The power conversionsystem of claim 16, wherein the output stage comprises an oscillatingcircuit configured to produce the output signal in the form of analternating current (AC) waveform.
 20. The power conversion system ofclaim 19, further comprising a plurality of transformers, eachtransformer comprising a first coil connected to a corresponding secondswitching stage and a second coil connected to the output stage.
 21. Amethod of converting power from an array of direct current (DC) powersources to alternating current (AC) power, the method comprising:converting DC power from each DC power source to a series of electricalenergy packets; combining the series of electrical energy packets fromeach DC power source to form a combined electrical energy packet signal;directing the combined electrical energy packet signal into anoscillating circuit to drive the oscillating circuit; and producing analternating current (AC) output signal via the oscillating circuit. 22.The method of claim 21, wherein directing the combined electrical energypacket signal into an oscillating circuit comprises directing thecombined electrical energy packet signal into an LC tank circuit. 23.The method of claim 21, wherein the combined electrical energy packetsignal has a frequency matched to a resonant frequency of theoscillating circuit.
 24. The method of claim 21, wherein converting DCpower from each DC power source to a series of electrical energy packetscomprises, for each DC power source: operating a first switching stagein a closed state while operating a second switching stage in an openstate thereby charging an intermediate charge storage stage locatedbetween the first switching stage and the second switching stage, andthen operating the second switching stage in a closed state whileoperating the first switching stage in an open state to release anelectrical energy packet from the intermediate storage stage.
 25. Themethod of claim 24, wherein charging the intermediate charge storagestage comprises transferring electrical charge from an initial chargestorage stage to the intermediate storage stage while the firstswitching stage is in the closed state.
 26. A power conversion system,comprising: a plurality of direct current (DC) power sources; aplurality of power output circuits connected to one another in aparallel arrangement, each power output circuit being connected to acorresponding DC power source to receive power from the corresponding DCpower source and to selectively discharge power received from thecorresponding DC power source; a power combiner configured to combinepower received from the plurality of power output circuits to form acombined power signal, wherein power received from each of power outputcircuits by the power combiner is substantially of a same polarity; anoutput stage configured to convert the combined power signal into an ACsignal or a DC signal; and a controller in electrical communication witheach power outlet circuit and the power combiner to control the outputof power by the power converter.
 27. The power conversion system ofclaim 26, wherein the power output circuits are configured to outputelectrical energy packets, wherein the power combiner is configured toform a combined energy packet signal, and wherein the output stagecomprises an oscillating circuit configured to be driven by the combinedenergy packet signal.